Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. The value of C.O.P in vapour compression cycle is usually

Equal to unity

Always less than unity

Always more than unity

Any one of the above

2. Highest temperature encountered in refrigeration cycle should be

Above critical temperature

At critical Temperature

Near critical temperature of refrigerant

Much below critical temperature

3. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Brine

Ammonia

Carbon dioxide

Freon

4. The condition of refrigerant after passing through the condenser in a vapour compression system is

Dry saturated vapour

Superheated vapour

Wet vapour

Saturated liquid

5. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Involves no change in volume

Takes place at constant temperature

Takes place at constant pressure

Takes place at constant entropy

6. The boiling point of ammonia is

-30°C

-10.5°C

-33.3°C

-77.7°C

7. The curved lines on a psychrometric chart indicates

Wet bulb temperature

Dry bulb temperature

Dew point temperature

Relative humidity

8. In a refrigeration system, the expansion device is connected between the

Condenser and receiver

Evaporator and compressor

Receiver and evaporator

Compressor and condenser

9. In a lithium bromide absorption refrigeration system

None of these

Water is used as a refrigerant and lithium bromide as an absorbent

Lithium bromide is used as a refrigerant and water as an absorbent

Ammonia is used as a refrigerant and lithium bromide as an absorbent

10. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 9

1: 3

1: 1

9: 1

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11. The domestic refrigerator uses following type of compressor

Centrifugal

Piston type reciprocating

Miniature sealed unit

Axial

12. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Normal cooling

Sub-cooling or under-cooling

Super-cooling

None of these

13. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Zero

Positive

None of these

Negative

14. Which of the following statement is correct?

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(D) Both (A) and (B)

(B) The increase in air movement increases the evaporation from the human body.

15. Critical temperature is the temperature above which

Water will never evaporate

A gas will immediately liquefy

A gas will never liquefy

Water will evaporate

16. Cooling water is required for following equipment in ammonia absorption plant

Condenser

Evaporator

Absorber

Condenser, absorber and separator (rectifier)

17. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

2.33

3.33

1.33

4.33

18. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(A) Heat dissipated to the surroundings

(B) Heat stored in the human body

(D) Difference of (A) and (B)

19. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

1.25

2.15

5.12

20. The vapour compression refrigerator employs the following cycle

Reversed Rankine

Reversed Carnot

Rankine

Carnot

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21. Which of the following is not a desirable property of a refrigerant?

Low boiling point

Large latent heat

Good electrical conductor

High risibility with oil

22. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.6

0.67

0.376

0.4

23. A thermostatic expansion valve in a refrigeration system

Is suitable only for constant load systems

Maintains different temperatures in evaporator in proportion to load

Ensures the evaporator completely filled with refrigerant of the load

None of the above

24. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Superheat the vapour

Collect liquid refrigerant and prevent it from going to compressor

Collect vapours

Detect liquid in vapour

25. The minimum temperature to which water can be cooled in a cooling tower is

Dew point temperature of air

Dry bulb temperature of air

Ambient air temperature

Wet bulb temperature of air

26. A bootstrap air cooling system has

One heat exchanger

Two heat exchangers

Four heat exchangers

Three heat exchangers

27. The freezing point of sulphur dioxide is

-75.2°C

-56.6°C

-135.8°C

-77.7°C

28. The bank of tubes at the back of domestic refrigerator is

Condenser tubes

Capillary tubes

Refrigerant cooling tubes

Evaporator tubes

29. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Unpredictable

Equally

Less

30. Rating of a domestic refrigerator is of the order of

0.1 ton

5 tons

10 tons

40 tons

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31. Freon group of refrigerants are

Inflammable

Nontoxic and non-inflammable

Toxic

Non-inflammable and toxic

32. For obtaining high COP, the pressure range of compressor should be

Any value

Optimum

Low

High

33. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

34. In a refrigeration system, heat absorbed in comparison to heat rejected is

Less

More for small capacity and less for high capacity

Same

35. The capillary tube, as an expansion device, is used in

Water coolers

Domestic refrigerators

Room air conditioners

All of these

36. The operating pressure for refrigerating units using R-12 as a refrigerant is

2 bar

8 bar

30 bar

15 bar

37. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

(T₂ - T₁)/T₁

(T₁ - T₂)/T₁

T₁ / (T₂ - T₁)

T₂/ (T₂ - T₁)

38. Which of the following cycles uses air as the refrigerant?

Carnot

Stirling

Bell Coleman

Ericson

39. Most thermostatic expansion valves are set for a superheat of

5°C

20°C

10°C

15°C

40. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

1.2

0.2

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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